As Canadian prime minister Harper and US President Obama prepare for their meeting in Washington today, 20 Greenpeace activists from Canada, France, and the US continue to blockade Shell’s Albian Sands open-pit mine in Canada's tar sands.

Shell shut down the entire operation of the mine. The activists have been in place for over 18 hours and are sending a message to Harper and Obama telling them "climate leaders don't buy tar sands".

"Tar sands are a climate crime and will certainly be a big part of the discussion between Obama and Harper. Obama needs to reject any further development of tar sands, and commit to weaning the US off of its dangerous addiction to oil. Only then can he become a true leader on climate change" said Mike Hudema, Greenpeace Canada climate and energy campaigner from inside the blockade.

Canada's tar sands cover an area larger than England. Developing the tar sands has created the largest industrial development project - and one of the biggest environmental crimes - on the planet. Plans for further development, driven largely by European companies producing for US markets, mean that the tar sands could emit between 127 and 140 million tonnes of greenhouse gas emissions a year by 2020, more than the annual emissions of Denmark.

In open pit mining operations like Shell's Albian Sands, vast swaths of forest are cut down and the land stripped for mining, to be replaced by a landscape of toxic lakes and massive mines. In "in situ" operations like those of Norway's Statoil and others, super-heated steam is injected deep into the earth to melt out the oil, burning enough natural gas to heat four million North American homes every day.

While Shell has the biggest operations in the tar sands, companies including BP, Suncor, Syncrude, ExxonMobil, Total and StatoilHydro are all heavily investing in the tar sands.

In December, the world has an historic opportunity to step back from the brink of catastrophic climate change. At the UN Climate Summit in Copenhagen, world leaders must agree urgent measures to save the climate (2). This means quitting the tar sands.

Notes: (1) for more detail about the climate impact of the tar sands see the Greenpeace report "Dirty Oil: How the tar sands are fueling the global climate crisis, by award winning author Andrew Nikiforuk available at http://www.greenpeace.org/canada/en/recent/tarsands_report

(2) At Copenhagen, governments must agree: Legally binding emission cuts for industrialised countries, as a group, of at least 40% below 1990 levels by 2020. Additionally, industrialised countries must make available at least USD 140 billion annually, to support clean energy and other mitigation activities, forest protection and adaptation in developing countries. 2) Mitigation actions for developing countries to achieve a 15-30% deviation from business as usual growth by 2020. 3) A funding mechanism to end gross deforestation in all developing countries by 2020, and achieving zero deforestation by 2015 in priority areas, such as the Amazon, the Congo Basin, and the Paradise forests.